A biopharmaceutical company that helped produce Dolly the sheep has produced new pig clones.

PPL Therapeutics says the pigs, which lack a specific gene, are a major step towards using animal organs for human transplants.

The female piglets were born on Christmas Day in the United States.

This advance provides a near term solution for overcoming the shortage of human organs for transplants

David Ayares, PPL

They have been named Noel, Angel, Star, Joy and Mary.

These are not the first pig clones, but PPL, a commercial offshoot of the Roslin Institute in Scotland, says the pigs are the first to be engineered in a way that should help prevent their tissues being rejected by the human body.

The animals' biological make-up is slightly different from ordinary pigs.

'Near term' solution

A specific gene, which makes the human body reject pig organs, has been "knocked out".

PPL says that it intends to use the pigs as part of its programme to seek a cure for humans suffering from diabetes.

It raises serious ethical issues over the use of animals and a major question of safety

Dr Donald Bruce, Church of Scotland

Dr David Ayares, Vice-President of Research at PPL's US division said the birth of the pigs was a critical milestone in the company's xenograft programme.

"This advance provides a near-term solution for overcoming the shortage of human organs for transplants as well as insulin-producing cells to cure diabetes," Dr Ayares said in a statement.

The news was given a cautious welcome by the Society, Religion and Technology Project of the Church of Scotland.

Safety concerns

Dr Donald Bruce said the disabling of a gene that would otherwise cause the rejection of a pig organ by the human body might, potentially, be ethically acceptable in the context of xenotransplantation but only if a number of conditions were fulfilled.

Genetically altered pigs are now a reality

"The prospect of using pig organs to save many human lives, or to improve substantially the quality of life of dialysis patients or diabetics, is attractive from the viewpoint of human medicine," he said.

"But it raises serious ethical issues over the use of animals and a major question of safety." He added: "The fact that we already eat pigs is not a sufficient moral argument. This would be an entirely new way of relating to animals. Switching organs across species represents a different way of using animals from anything humans have done before."

PPL was the first to clone pigs in spring 2000. In April 2001, PPL said that it had produced gene-altered, or transgenic, pig clones.

The pigs had had a foreign gene added to the cells from which they were developed.

A month later an Australian company, BresaGen Ltd, said it had also produced a pig clone using a different technology.

Potential obstacles

Pigs are thought by some scientists to be the most suitable animals for providing organs for transplant into humans.

A pig's heart is about the same size as a human's and has about the same power output.

Furthermore, scientists think they understand the steps they need to take to genetically modify pig tissue so that it will not be rejected by the human immune system.

However, there are a number of major problems yet to be overcome. These include the theoretical risk that pig viruses might jump into humans and cause new diseases.

Sarah Kite, from the British Union for the Abolition of Vivisection, was critical of the development, saying that many animals were being put through horrific and pointless experiments.

"We believe this is yet further scientific hype because it is leading people to falsely believe that successful animal transplants are just around the corner," she told the BBC.

She said scientists still did not understand the rejection issue properly and added that there were major doubts over whether animal organs could sustain human life.

"The full potential for getting human donor organs has not yet been realised. We still haven't got an 'opt out' system in this country where humans are assumed to want their organs used for transplant after their death."